The packaging and labeling arts have long used heat shrinkable plastic tubing, typically polyvinylchloride (PVC) or polyethylene, for the purposes of quickly and efficiently banding together multiples, groups or combinations of products and/or in labeling products of any shape or securing promotional premiums or the like to articles. The heat shrinkable bands or labels employed heretofore have been manufactured primarily as seamless tubing, by pneumatically expanding a continuously formed hollow cylinder of PVC or polyethylene and then permitting the expanded cylinder to be cooled. The resulting tubing has a "memory" and will shrink radially and longitudinally upon the subsequent application of heat thereto. Alternatively, heat shrinkable tubing has been formed by taking flat sheets or webs of heat shrinkable PVC or other heat shrinkable material and folding the same into a flat folded "tube" or band by connecting the free ends by a sealed seam or joint.
Disclosed herein is a new and improved method of continuously forming a heat shrinkable packaging medium from PVC tubing comprising the steps of supporting a roll of flat folded heat shrinkable seamless tubing material for controlled unwinding; directing a web of tubing drawn from said roll toward a sealing station; directing said unseamed tube to an ultrasonic welding station; applying ultrasonic welding energy exteriorly and transversely of said tube for less than the full width thereof while pinching the walls thereof between an ultrasonic horn means bearing against lower exterior surfaces of said tubing and a sealing bar means bearing against the upper surfaces of said tubing to weld said walls into a permanent joint and to form an air relief port; advancing the welded tube from said welding station to a severing station; severing said tubing downstream of said joint to separate an individual bag having an open end and closed end.
The resulting heat shrinkable tubular element comprises a shrinkable PVC bag having juxtaposed top and bottom walls, the sides of which are the parallel fold lines of tubing; the ultrasonically established weld permanently joining said top and bottom walls along a first edge; and an open end at a second edge opposite said first edge; the air relief port permitting trapped air to escape from the element when it is heat shrunk over an irregularly shaped object.
For a better appreciation of the principles of the present invention and a more complete understanding of its attendant advantages, reference should be made to the following detailed description of the invention taken in conjunction with the accompanying drawings.